The present invention relates to a method for forming a wiring structure in a semiconductor device.
As a conventional method for forming a wiring structure, there has been used one disclosed in, e.g., Japanese Laid-Open Patent Publication No. HEI 10-214834. Referring to the drawings, the conventional method for forming a wiring structure will be described by using, as an example, the case where plugs are formed in holes formed in an insulating film.
FIGS. 9A to 9C are cross-sectional views illustrating the individual process steps of the conventional method for forming a wiring structure.
First, as shown in FIG. 9A, a silicon dioxide film 12 having a thickness of about 1 xcexcm is deposited as an insulating film on a silicon substrate 11. Then, holes 13 each having a diameter of about 0.8 xcexcm are formed by lithography and dry etching in specified regions of the silicon dioxide film 12 to extend therethrough.
Next, a titanium film 14 having a thickness of 30 nm and serving as a lower-layer conductive film and a titanium nitride film 15 having a thickness of 100 nm and serving as an interlayer conductive film are deposited successively by PVD (physical vapor deposition) over the entire surface of the silicon dioxide film 12 including the holes 13. Thereafter, a tungsten film 16 having a thickness of 1 xcexcm and serving as an upper-layer conductive film is deposited by CVD (chemical vapor deposition) over the entire surface of the titanium nitride film 15, whereby a conductive film having a three-layer structure is deposited. In the three-layer conductive film, each of the titanium film 14 and the titanium nitride film 15 is a barrier metal.
Next, the respective portions of the tungsten film 16 and the titanium nitride film 15 deposited on regions outside the holes 13 are removed by chemical mechanical polishing (CMP) using an abrasive agent, as shown in FIG. 9B. This completely exposes the portions of the titanium film 14 deposited on the regions outside the holes 13.
Next, the portions of the titanium film 14 deposited on the regions outside the holes 13 are removed by CMP using another abrasive agent, as shown in FIG. 9C. This forms plugs 17 composed of tungsten in the holes 13 and exposes the silicon dioxide film 12.
Although the formation of tungsten plugs has been described above by way of example, it is also possible to form, e.g., copper wires in wiring grooves formed in an insulating film by the same method.
With the scaling down of a wiring pattern, the spacing between adjacent wires (wire-to-wire spacing) has been reduced increasingly so that an anti-reflection layer (hereinafter referred to as ARL) has been used in a lithographic step for forming wiring grooves, via holes, and the like.
However, the formation of wires using an ARL film based on the foregoing conventional method for forming a wiring structure has the problem that a short circuit occurs between wires.
It is therefore an object of the present invention to prevent a short circuit between wires buried in an insulating film and in an ARL film on the insulating film.
To attain the object, the present inventors have examined causes for the short circuit occurring between the wires in the conventional method for forming a wiring structure and made the following finding.
In forming wires in accordance with the conventional method for forming a wiring structure, a barrier metal under polishing locally peels off to form a foreign matter. Since the foreign matter is hard, if an ARL film composed of a material more fragile than an insulating film present between wires has been formed on the insulating film, the foreign matter causes a microcrack in a surface of the ARL film. In the case where the microcrack extends from one wire to another wire adjacent thereto, if a metal (the barrier metal or a conductive film) is buried in the microcrack during the formation of wiring, a short circuit occurs between the wires.
Since the spacing between wires is reduced as the wiring structure is scaled down, the microcrack mentioned above is more likely to extend between the adjacent wires so that the metal buried in the microcrack is more likely to form a pseudocross-linking structure between the wires. As a result, a short circuit is more likely to occur between the wires.
FIG. 10 is a plan view showing the metal buried in the microcrack caused in the ARL film between the wires. As shown in FIG. 10, a plurality of copper wires 22 are buried in an ARL film 21 in such a manner as to extend in parallel with each other. A crack 23 has been formed in the ARL film 21 between the copper wires 22 in such a manner as to extend therebetween. Copper was buried in the crack 23 during the formation of the copper wires 22 so that a short circuit occurs between the copper wires 22.
The present invention has been achieved in view of the foregoing finding. Specifically, a method for forming a wiring structure according to the present invention comprises: a groove forming step of forming an anti-reflection film on an insulating film and then forming, in each of the anti-reflection film and the insulating film, a first groove and a second groove adjacent to the first groove; a film depositing step of depositing a barrier metal film and a conductive film on the anti-reflection film such that each of the first and second grooves is filled therewith; a first polishing step of removing the portion of the conductive film outside the first and second grooves by polishing; a second polishing step of removing, after the first polishing step, the portion of the barrier metal film outside the first and second grooves by polishing; a foreign matter removing step of removing a foreign matter adhered to a surface to be polished after the second polishing step in the second polishing step therefrom; and a third polishing step of polishing, after the foreign matter removing step, a surface of the anti-reflection film.
In the method for forming a wiring structure according to the present invention, the barrier metal film and the conductive film are buried in the grooves formed in the insulating film and in the anti-reflection film on the insulating film and then the respective portions of the conductive film and the barrier metal film outside the grooves are removed by polishing. Thereafter, the foreign matter adhered to the surface to be polished during polishing is removed and then the surface of the anti-reflection film is polished. This achieves the following effects if a microcrack is formed in the surface of the anti-reflection film present between the grooves (i.e., between wires) during the polishing of the barrier metal film and a metal is buried in the microcrack. Since final polishing is performed with respect to the surface of the anti-reflection film after the foreign matter adhered to the surface to be polished during the polishing of the barrier metal film or the like is removed therefrom, it is possible to remove the metal buried in the microcrack, while preventing new damage caused by the foreign matter to the surface of the anti-reflection film. This allows the situation in which the metal buried in the microcrack causes cross-linking between the wires to be circumvented and thereby reduces the frequency of short circuits occurring between the wires. As a result, high-performance wiring can be formed.
Preferably, the method for forming a wiring structure according to the present invention further comprises, between the second and third steps, the step of removing a foreign matter adhered to a polishing pad used in the second polishing step therefrom.
The arrangement more reliably prevents damage to the surface of the anti-reflection film if the polishing pad used in the second polishing step (polishing of the barrier metal film) is used in the third polishing step (polishing of the anti-reflection film). In this case, if the step of removing the foreign matter adhered to the polishing pad therefrom includes the step of cleaning the polishing pad, damage to the surface of the anti-reflection film can be prevented more reliably. The same effect is achievable if the step of removing the foreign matter adhered to the polishing pad therefrom includes the step of brushing a surface of the polishing pad with a grindstone.
In the method for forming a wiring structure according to the present invention, each of the second and third polishing steps is preferably performed by using the same polishing system and the same polishing pad.
The arrangement improves work efficiency in the formation of wiring.
In the method for forming a wiring structure according to the present invention, a pressure under which the surface to be polished is pressed onto a polishing pad and a rotating speed of the polishing pad in the third polishing step are preferably the same as in the second polishing step.
The arrangement obviates the necessity to make intricate changes to polishing conditions in a transition from the second polishing step to the third polishing step. Accordingly, work efficiency in the formation of wiring is improved and a reduction in process throughput is thereby prevented. If the polishing time is shorter in the third polishing step than in the second polishing step, the surface of the antireflection film is prevented from being significantly scraped off. If the foregoing pressure and rotating speed are lower in the third polishing step than in the first polishing step, the significant scraping-off of the surface of the anti-reflection film can be prevented more reliably.
In the method for forming a wiring structure according to the present invention, an abrasive agent used in the third polishing step is preferably the same as used in the second polishing step.
The arrangement prevents the conductive film buried in the grooves from being significantly polished in the third polishing step so that an increase in wiring resistance is prevented.
In the method for forming a wiring structure according to the present invention, the third polishing step may include a polishing step performed in two stages under different polishing conditions. In this case, an abrasive agent used in one of the two stages of the polishing step is preferably the same as used in the second polishing step and an abrasive agent used in the other of the two stages of the polishing step is preferably the same as used in the first polishing step. The arrangement improves a yield rate in the formation of wiring.
In the method for forming a wiring structure according to the present invention, the foreign matter removing step preferably includes the step of cleaning the surface to be polished by using an organic acid or an organic alkali.
The arrangement ensures the removal of the foreign matter adhered to the surface to be polished.
In the method for forming a wiring structure according to the present invention, if a spacing between the first and second grooves is 0.25 xcexcm or less, the present invention more remarkably achieves the foregoing effects than the prior art.
In the method for forming a wiring structure according to the present invention, the first and second grooves may be arranged in parallel with each other.
In the method for forming a wiring structure according to the present invention, formation of wires in the first and second grooves may be performed by a dual damascene method.
In the method for forming a wiring structure according to the present invention, the anti-reflection film may be composed of a silicon containing material.
The arrangement ensures an improved accuracy with which a pattern is formed in a lithographic step for forming the grooves. If a KrF excimer laser beam (at a wavelength of 248 nm), e.g., is used as a light source in the lithographic step, a multilayer film consisting of a lower-layer SiON film having a thickness of 75 nm and an upper-layer SiO2 film having a thickness of 8 nm exhibits a high absorption efficiency to the KrF excimer laser beam so that the multilayer film has excellent performance as an anti-reflection film. If a silicon compound is used as a material composing the anti-reflection film, equipment for forming a hole in the silicon dioxide film can be used commonly as equipment for forming a hole in the anti-reflection film, which achieves a reduction in fabrication cost for the semiconductor device.
In the method for forming a wiring structure according to the present invention, the conductive film is preferably a copper film and the barrier metal film is preferably a tantalum film, a tantalum nitride film, or a multilayer film composed of a tantalum film and a tantalum nitride film.
The arrangement allows the formation of low-resistance wiring. In this case, a wire formed in the first or second groove may be connected electrically to a plug formed under the wire.